A. Field of the Invention The present invention relates to changing operating power to a high-intensity discharge (HID) lamp by adding (or removing) capacitance, and in particular, by incrementally adding (or removing) capacitance at predetermined, separated times.
B. Problems in the Art
U.S. Pat. No. 7,176,635, entitled “Apparatus and Method for Compensating for Reduced Light Output of a Light Source Having a Lumen Depreciation Characteristic Over Its Operational Life” describes one approach for changing operating power to an HID lamp by changing capacitance in the lamp circuit. U.S. Pat. No. 7,176,635, incorporated by reference in its entirety herein, also discusses why changing operating power can be beneficial to operation of such lamps and why changing capacitance is an economical, efficient, and effective way of doing so. A commercial version is available from Musco Corp., Oskaloosa, Iowa USA under the trademark SMART LAMP®. As explained in U.S. Pat. No. 7,176,635, one purpose of additional operating power is to compensate for lamp lumen depreciation (LLD) that occurs in most of these types of lamps.
One embodiment in U.S. Pat. No. 7,176,635 uses a very robust, low cost, low complexity combination of components. In the first embodiment, an electric timer motor rotates cams that, in turn, actuate switches, relays or contactors to sequentially switch capacitors to increase capacitance to the lamp circuit at times determined by the electric timer motor and cams. The elegance of this solution is that the timer motor is electrically connected into the lamp circuit. It only runs when the lamp is operating. Therefore, it does not run constantly, but rather keeps track of cumulative operating time of the lamp.
As explained in U.S. Pat. No. 7,176,635, one use of such circuits is for sports lighting. A sports lighting system has a normal effective life of decades, and over those decades the lights are normally operated for thousands of hours, usually for three to five hours a day at most. The electrical timer/cam combination thus is energized (provided electrical power) whenever the lamp is energized. The cams rotate very slowly and are preconfigured to rotate to a position that operates a switch at a predetermined time when additional capacitance to the lamp is desired to provide additional operating power to the lamp.
The electromechanical solution of the electric timer motor/cam is not only economical, but is quite robust. The combination is similar to combinations in use for decades in washing machines. As a mass market consumable, cost of washing machines is a critical purchasing decision factor. The electric motor/cam combination controls the various states and cycles of a washing machine, and has been developed over time to be a widely used, reliable, and economical component. A washing machine exposes its components to substantial vibration and moisture over its expected life (also decades). These conditions are similar to what sports lighting experiences—vibration from wind and other forces, as well as rain, snow, wind, temperature extremes, etc.; although outdoor lighting systems experience more dramatic forces, including lightning, since they usually have metal parts elevated high above the ground. An electromechanical solution for switching in or out capacitance in a sports lighting system was discovered to be economical but also robust for outdoors environments, especially that it is much more resistant to damage or effect by lightning than electronic components.
In addition to the first embodiment disclosed, U.S. Pat. No. 7,176,635 discloses other ways in which an electrical timer motor could change operating power to the lamp through changing of capacitance. Some involve somewhat more complexity and cost, but they predominantly rely upon an electromechanical timer motor/cam combination.
Systems are known for changing operating power of other types of lamps or light sources, or other devices. For example, a number of publications disclose ways of adjusting operating power to indoor florescent light fixtures. They usually use electronic components, at least in part, are intended for indoor operation, and thus are not exposed to substantial moisture, vibration, or lightning. They also are usually not intended for high wattage or high power. Therefore, different considerations control those designs.
Therefore, although U.S. Pat. No. 7,176,635 presents solutions that work reasonably well, and power-adjustment systems for other types of lamps or devices use more electronic solutions, it is apparent that for wide-area, high power HID lighting there are many factors that must be considered, and they can differ dramatically from indoor lighting or device solutions. Thus, there is room for alternative solutions for practical power adjustment of HID light sources, fixtures, and systems.
The present invention speaks to alternative solutions to changing operating power to an HID lamp by changing capacitance in the lamp circuit.